WAM/MLAT Algorithm

WAM algorithm is a hyperbolic positioning algorithm, the basic equation shown at right. If the number of base stations over four, the basic equation for thesuper-set equation to convert non-overdetermined equation by the least squares method.

WAM/MLAT Algorithm Theoretical derivation can be

drawn, multi-point positioning precision and accuracy of time difference relationship for the approximate linear relation, matrix G directly influences the positioning precision, while the matrix G by the site location and positioning point position is decided jointly.

According to GPS positioning theory, can introduce HDOP / VDOP factor to describe the MLAT/WAM error distribution.

According to statistics, ultimately need to get 95% confidence level error, can be expressed as:

EPU = 1.96HDOP δ

TEDC WAM/MLAT • TEDC ADSB-2000A provides two types of Multilateration

model:– WAM mode used for time synchronization methods, through

the GPS ( the future use of the COMPASS) time, by base stations (time synchronization accuracy needs to be controlled within 100ns ).

– Surface monitoring Multilateration using independent transmitter with high precision timing, the TEDC ADSB-2000A device can provide the highest 1ns timing precision (theoretical value of up to 0.3 meters), taking into account the crystal temperature drift, base station position measurement error, baseband pulse measurement and other reasons, the system in the best condition base station layout, the design accuracy requirements for RMS 10 metres.

TEDC WAM/MLAT

DSP Core2（去交织）

FPGA

（

数据

预处

理

）

ADC

ADC

DSP Core0（同步检测）

DSP Core1（去交织）

10ms 数 据流

5ms数

据流

5ms数

据流

连续数据流

接收通道2

接收通道1

L2 处理单元有效数据

有效数据

TEDC WAM

• TEDC WAM based on TEDC ADSB-2000A receiver equipment R & D, consists of the following components:– The ADSB-2000A receiver (3 above )– 10W 1090ES transmitter– Central processing computer– Data output interface device– The optional 1030MHz rotary inquiry machine

TEDC WAM• TEDC has carried on

many times the multilateration test, the car station in Beijing Daxing District, Hebei Xiongxian, Hebei Cangzhou, Hebei Dingzhou built four remote multilateration station.

• Test contains the 1090MHz ModeS, Mode A / C and ADS-B ( out ) frame .

TEDC WAM

TEDC WAM

TEDC WAM

ADS-B Security

• ADS-B data security is the basic problem:– Air Ground transmission reliability ( transmission

delay, crosstalk, interweaves wait for a problem )– False target and electronic jamming.– GNSS system integrity loss / failure and ADS-B Out

alternative surveillance technology.

ADS-B Security

遮挡，交织或者串扰引起的ADS-B掉点现象

ADS-B Security

正常 ADS-B位置外推及延迟

位置外推异常或延迟不规范

ADS-B Security

正常的 ADS-B雷达联合航迹

误差较大的 ADS-B雷达联合航迹

ADS-B Security

某些飞行器（红色）， NUCp值恒小于 4

飞行器的 NUCp值从大于 7 过度到小于 7 ，但临近飞行器保持在7 以上

ADS-B Security

• ADS-B data security problems:– ADS-B data reliability.– ATC system’s fusion model.– ADS-B data transmission and usability problems.

ADS-B Security

• ADS-B data reliability problems– Airborne ADS-B apparatus is provided to position

the confidence degree ( NUCp ) may not be entirely reliable, different aircraft in the same region of the same moment may have a different location confidence value.

– As a result of airborne equipment and firing pattern of inconsistency, leading to ADS-B position data is not accurate

ADS-B Security

From the statistics, NUCp value mainly concentrated in the5,6,7, but a large proportion of the data NUCp 0, NUCp 0means that the ADS-B position data is invalid.

ADS-B Security

• ATC system security issues (for processing ADS-B data)– Unproven ADS-B track directly into the automated system

position accuracy and transmission delay of dual risk.– Position risk is airborne equipment NUCp inconsistency,

may lead to some lost tracks, or to produce incorrect track.– Transmission delay will lead to automatic velocity tracking

system instability condition, serious cases will affect the tracking accuracy.

ADS-B Security

• Extended ADS-B ground station, through the regional centralized processing can solve the ADS-B security problems.

• ADS-B ground station should provide precise timing function, the use of precision timing, without changing the construction scale of the circumstances, can greatly improve the security questions of ADS-B data.

• Regional centralized processing is the current ADS-B construction is necessary and urgent problem, through the regional centralized treatment, can improve the ADS-B ground station network capacity, and provides additional functionality.

ADS-B Security

ADS-B Corroboration ：

ADS-B Security

ADS-B Security in H15

ADS-B Security

ADS-B Security in H15

ADS-B